Such requirements as Gbps-level transmission rate, ultrahigh flux density, huge connections, increased spectral efficiency and reduced time delay have been put forward for a 5th-generation (5G) mobile communication system. An IMT-2020 (5G) promotion group in China has proposed four typical application scenarios for the 5G mobile communication system, i.e., an application scenario with wide-area coverage and an application scenario with hotspot, large-capacity coverage with respect to a mobile Internet application, and an application scenario with low-power-consumption, large connection and an application scenario with low time delay and high reliability with respect to a mobile Internet of Things (IoT) application.
Currently, the 3rd-Generation Partnership Project (3GPP) has initiated MultiUser Superposition Transmission (MUST), which mainly focuses on the application of a non-orthogonal multiple access technology to downlink transmission and the use thereof to increase the spectral efficiency. Essentially, the MUST is a mobile Internet scenario-oriented application.
A principal challenge for a 5G mobile Internet business application lies in an increase in the transmission rate, usually with large-scale antenna array, ultra-dense networking and high-frequency communication as main technical means and with the non-orthogonal multiple access technology as a strengthening way. A principal challenge for a 5G IoT business application lies in a huge number of connections.
For the 5G mobile IoT application scenarios with a large number of connections, low time delay and high reliability, in the case that an uplink scheduling algorithm for a conventional 4G system continues to be used, a large number of control signaling overheads are required. In the case that the number of the connections reaches a certain value, the number of User Equipments (UEs) scheduled by the system is limited to control channel resources.
In a word, for the 5G application scenarios, in the case that the uplink scheduling algorithm for the conventional 4G system continues to be used, a large number of control signaling overheads are required due to the meteoric growth in the number of the UEs to be connected.